There is known an image generation device that maps an input image from a camera on a predetermined space model on a three-dimensional space, and generates a visual point conversion image, which is viewed from an arbitrary virtual visual point in the three-dimensional space while referring to the mapped space data (for example, refer to Japanese Patent Publication No. 3286306).
The image generation device disclosed in Japanese Patent Publication No. 3286306 projects an image taken by a camera mounted on a vehicle onto a three-dimensional space model configured by a plurality of plane surfaces or curved surfaces that surround the vehicle. The image generation device generates a visual point conversion image using the image projected onto the space model, and displays the produced visual point conversion image to a driver. The visual point conversion image is an image of a combination of a road surface image, which virtually reflects a state of a road taken from directly above, and a horizontal image, which virtually reflects a horizontal direction image. Thereby, the image generation device can relates, when the driver driving the vehicle looks the visual point conversion image, an object in the visual point conversion image to an object actually existing outside the vehicle without giving uncomfortable feeling.
The image generation device disclosed in Japanese Patent Publication No. 3286306 generates a view point conversion image using an image projected on a three-dimensional space model. Therefore, for example, in a case of using a cylindrical space model arranged in a circumference of a vehicle, an effective view point conversion image can be generated when a virtual view point is set, which is on a center axis of the cylinder and views the cylinder from directly above. However, when a virtual view point is set, which is on a center axis of the cylinder and views the cylinder from directly above, an image projected on an inner side surface thereof (an image which is a base of a horizontal image in the vie point conversion image) cannot be displayed at all. Or, when a virtual camera which views the side surface of the cylinder from outside is set, an image projected on an inner bottom surface of the cylinder (an image which is a base of a road surface image in the view point conversion image) and an image projected on an inner side surface thereof (an image which is a base of a horizontal image in the vie point conversion image) cannot be displayed at all. Therefore, a position of the virtual camera, which can be set, is limited to a large extent.
Moreover, the image generation device disclosed in Japanese Patent Publication No. 3286306 generates the view point conversion image by regarding an image projected on a space model as a nondivisible one piece unit. For example, when a cylindrical space model arranged around a vehicle is used, even if it is desirable to enlarge or reduce only an image projected on an inner side surface of the cylinder (an image which is a base of a horizontal image in the view point conversion image), the generation of the view point conversion image must be performed again by changing a position or an angle of view of the virtual camera. Thereby, an influence is given to an image projected on an inner bottom surface of the cylinder (an image which is a base of a road surface image in the view point conversion image). Thus, the image generation device disclosed in Patent Document 1 lacks flexibility in adjusting a view point conversion image.